Cooper



Feb. 14, 1956 c. COOPER, JR

THERMOSTATIC SWITCH Filed June 5, 1954 v11" 7 Mum mam IN V EN TOR.

0 LEE K c OOPERJ JR.

United States Patent THERMOSTATIC SWITCH Clark Cooper, Jr., Moorestovvn, N. J., assignor to Scaico Controls, Inc, Palmyra, N. 1., a corporation of New Jersey Application June 3, 1954, Serial No. 434,201

10 Claims. (Cl. 200-437) This invention relates generally to thermostatic switches using thermally-responsive actuating elements and more particularly to such a thermostatic switch the housing or frame of which constitutes the thermallyn'esponsive actuating element of the switch.

A principal object of the present invention is to provide a thermostatic switch as aforementioned wherein a pair of tensioned members which respectively mount normally closed switch contacts are interconnected in an improved manner by a compressed member, the aforementioned tension and compression members being operative to open the contacts when the housing or frame expands due to a rise in temperature above normal.

Another object of the present invention is to provide a thermostatic switch of the character aforementioned wherein novel provision is made against excessive bending of the contact mounting members.

Still further objects of the present invention are to provide a compact, simple and economical form of thermostatic switch of the character aforementioned which has high thermal sensitivity, is very rugged and is exceptionally unresponsive to vibration forces.

Other objects and advantages of the present invention will appear more fully hereinafter, it being understood that the invention consists substantially in the combination, construction, location and general arrangement of parts, all as described in detail in the following specification, as shown in the accompanying drawings and as fully pointed out in the appended claims.

in the accompanying drawings:

Figure l is a longitudinal section through a thermostatic switch embodying the present invention, the switch contacts being shown closed;

Figure 2 is similar to Figure 1 but shows the switch contacts open;

Figures 3 and 4 are sections taken respectively on lines 3-3 and 44 of Figure 1; and

Figures 5 and 6 are diagrammatic views which illustrate the action of the switch contact mounting parts, Figure 5 showing the switch contacts closed and Figure 6 showing the switch contacts open.

The thermostatic switch as constructed in accordance with and embodying the principles of the present invention essentially includes an assembly of three strut members, the outer two of which are disposed in generally parallel relation and are secured together by the third member disposed intermediate of and extending angularly with respect to the outer members, the latter being extended beyond one end of the intermediate member to respectively provide laterally spaced supports for a pair of contacts 10 and 11. These contacts and their supporting strut assembly are operatively disposed within a suitable housing or frame which forms a constituent part of the switch unit.

The housing or frame is generally in the form of a tubular main body 12 made of material which has a high coeflicient of expansion, such as brass. The opposite head and foot ends of the main body 12 are closed respectively by internally fitted members 13 and 14 suitably secured against movement axially of the housing.

The outermost struts of the above mentioned assembly, respectively designated by the numerals 15 and 16, are preferably each formed of a material having a very low coefiicient of thermal expansion, such as Invar. These contact-carrying members 15 and 16 are in the form of relatively thin, flat strips having a certain degree of flexibility and are disposed in laterally spaced, generally parallel planes, the member 15 being anchored to the end member 13 at the head end of the housing 12, while the member 16 is anchored to the end member 14 at the opposite foot end of the tubular housing.

For anchoring the member 15, the latter is provided with a pin 17 which is rigidly secured thereto, and which extends in longitudinal continuation thereof. The pin 17 is threaded into an adjusting screw 18 which in turn is threaded into a sleeve 19, the latter being suitably rigidly secured to the member 13. A reduced diameter portion of the sleeve 19 is projected through the member 13 and into the housing 12. The shoulder formed by the change in diameter is seated against the outer face of the member 13, and the reduced diameter portion is provided with a diametrically extending open slot 20 which shiftably receives the terminal portions of the flexible member 15 on opposite sides of the pin 17. The free end portion of the flexible member 15 is set back only a short distance from the member 14 at the foot of the housing 12.

The base of the flexible member 16 is bent to provide angularly related parts 21 and 22, the former of which is seated upon the member 14 at the foot end of the housing 12 and suitably rigidly secured thereto for anchoring the flexible member 16 in the position shown so that the parts 21 and 22 extend around the free end portion of the flexible member 15.

The intermediate strut of the above mentioned assembly is in the form of a rigid flat bar member 23, preferably formed of Inconel or other material which, while having a low coeflicient of thermal expansion, is highly resistant to flexing and so may be considered relatively inflexible. The main body of this member 23 is disposed in a plane which extends obliquely with respect to and intersects the normally parallel planes of the outer strut members 15 and 16. The opposite end portions 23 -23 of the relatively inflexible intermediate member 23 are turned out of the plane of the main body thereof and are respectively rigidly secured, as by welding, brazing or otherwise, fiatwise against the free end portion of the flexible member 15 and an intermediate portion of the flexible member 16.

The switch contacts 10 and 11 are conventionally mounted respectively on the flexible members 15 and 16 through the medium of insulating elements 2424 and are provided with lead wires 25-45 which extend through insulating elements 26-26 mounted in the member 13, It will be noted that the arrangement of parts is such that the member 16 projects a substantial distance beyond its point of securement to the end portion 23 of the intermediate inflexible member 23 to provide a cantilever support 16 for the contact 10 which is so resiliently biased as to normally maintain the contact 10 in engagement with the contact 11 mounted on the member 16.

It will be understood that prior to final adjustment of the thermostatic switch for operation thereof at a predetermined temperature, the contacts 10 and 11 will have been resiliently biased into engagement with one another with considerable force. Thereafter, the adjusting screw 18 is threaded into the sleeve 19, whereupon, as the adjusting screw 18 is turned upon the pin 17 and into the sleeve 19, the pin 17 is drawn into the ad justing screw 18. The former is provided with large pitch threads while the latter is provided with comparatively small pitch external threads, as a consequence of which the pin 17 and the flexible member 15 shift axially toward the head end of the housing 12, thereby initially placing the flexible members 15 and 16 each under tension and the inflexible intermediate member 23 under compression. The aforementioned force with which the contacts 10 and 11 initially engage one another is then reduced by suitably adjusting the screw 13, so that said contacts remain closed only so long as the temperature remains at or below a predetermined value.

In the use of the thermostatic switch, when the temperature rises above that for which the switch has been set, the main body 12 of the housing expands, as a consequence of which the flexible members 15 and 16 are subjected to increased tension, while the intermediate relatively inflexible member 23 is correspondingly subjected to increased compression, resulting in opening of the contacts as shown in Figure 2. It will be understood, of course, that so long as the temperature remains above the predeterminedly established contact-opening temperature, the contacts will remain open and will be closed only when the temperature is at or below that for which the switch is set.

The action of the switch parts is diagrammatically illustrated in Figures 5 and 6, wherein it will be observed that the relatively inflexible intermediate member 23 is represented as being of rectangular block form, the opposite ends of which are respectively connected to the flexible members 15 and 16 which per se provide flexion connections With the intermediate relatively inflexible member 23. These flexion connections, each located immediately adjoining an end of the member 23, as at the points a and b in Figures 1 and 2, which flexion points are correspondingly designated a and b in Figures 5 and 6, permit angular displacement of the inner member 23 relatively to the outer flexible members 15 and 16 when the latter are subjected to tension forces rectilinearly applied while said members are maintained substantially parallel as shown. Upon the application of such tension forces to the members 15 and 16, the intermediate member 23 is caused to turn counter-clockwise from its normal position shown in Figures 1 and 5 in consequence of which the freely projecting portion 16 of the member 16 which serves as a cantilever support for the contact 11 bends angularly with respect to the main body portion of the member 16 to thereby separate the contact 11 from the contact 10 supported by the opposite flexible member 15. It will be understood, of course, that the tension forces applied to the members 15 and 16 to angularly vary the disposition of the intermediate member 23 are those which result from expansion of the casing 12 due to rise in temperature.

It will be noted that the freely projecting end of the flexible member 15 terminates short of the end member 14 of the casing 12 and is normally disposed in laterally spaced relation to the inwardly projecting part 22 of the secured end 21 of the flexible member 16. This part 22, which may be provided otherwise than as an integral part of the member 16, as, for example, by making it a part of the end member 14, serves primarily to limit the permissible transverse movement of the member 15 in a direction away from the member 16 so as to prevent any possibility of stressing said member 15 beyond its elastic limit. In normal operation of the switch, the freely projecting end of the member 15 and the corresponding end of the intermediate member 23 will conjointly float within the space 26 formed between the secured end of the member 16 and the inwardly projecting part 22, the position assumed by this floating end of the switch assembly within the space 26 being dependent upon the variations in temperature above that for which the switch has been initially adjusted. It will be apparent, of course,

that should the rise in temperature be such as to cause the normally floating end of the switch assembly to engage the part 22 to thereby restrain the member 15 from further movement away from the secured end of the member 16, the freely projecting portion 16 of the latter may continue to shift out of contact-closing position until restrained by the external casing 12.

The construction of the switch as shown in Figures 1 and 2 and as hereinabove described is of the type in which the contacts open upon expansion of the casing due to a rise in temperature. Obviously, substantially the same construction could be employed for closing the contacts upon expansion of the casing due to a rise in temperature, in which case the contact 10 would be removed from the member 15 and instead be suitably mounted upon the casing 12 in opposition to a contact suitably mounted upon the outer face of the cantilever extension 16 of the member 16. The switch would then be normally set so that at a predetermined temperature the contacts would close and remain so only as long as the temperature remained at or above said predetermined value.

While in the switch as hereinbefore described the strut members 15 and 16 are under constant tension, in consequence of which any increase in their tension due to expansion of the casing 12 will cause the contacts to open (or to close in the case of a switch having its contacts disposed for closing upon rise in temperature above a predetermined setting), it will be apparent that by placing the strut members 15 and 16 initially under compression with the contact members 10 and 11 just out of engagement with each other, upon contraction of the casing due to a drop in temperature below that for which the switch is set, the strut members 15 and 16 will be subjected to increased compression resulting in closing of the contacts. Thus the switch of the present invention may be designed for operation as a regular type for opening or closing of the contacts upon a rise in temperature, in which case the struts 15 and 16 are constantly under tension, or it may be designed for operation as a reverse type for closing the contacts upon a drop in temperature below a predeterminedly set point, in which case the outer strut members 15 and 16 are constantly under compression while the intermediate member 23 is under tension.

It will be noted that by reason of the rigidity of the member 23 and its connections with the flexible members 15 and 16, the latter are exceptionally unresponsive to vibration forces, as a consequence of which the switch is very sensitive, being able to hold a break point contact with very little pressure between the contacts.

It will be understood, of course, that the thermostatic switch hereinabove shown and described is susceptible of various changes and modifications which may be made from time to time without any departure from the general principles or real spirit of the invention. Accordingly, it is intended to claim the present invention broadly, as well as specifically, as indicated in the appended claims.

What is claimed as new and useful is:

1. A thermostatic switch comprising a tubular housing made of material having a high coefficient of expansion, an assembly of members disposed within said housing along the length thereof and made of material having a relatively low coeflicient of expansion, and switch contacts carried by said assembly of members and engaging one another, said assembly including first and second laterally spaced flexible members anchored respectively to the head and foot ends of said housing, and a substantially rigid member extending from a free end portion of said first flexible member toward said housing head and second flexible member, one end portion of said rigid member being rigidly secured to said free end portion of said first flexible member and being movable therewith laterally away from said second flexible member and the opposite end portion of said rigid member being rigidly secured to an intermediate portion of said second flexible member and being movable therewith laterally away from said first flexible member, said switch contacts being mounted respectively on a free end portion of said second flexible member and an intermediate portion of said first flexible member at a substantial distance from said relatively rigid member.

2. A thermostatic switch as defined in claim 1 wherein the connection between the substantially rigid member and the first flexible member is disposed in close proximity to the foot end of the housing, and the connection between said rigid member and the second flexible member is disposed approximately midway between the opposite ends of the housing so as to characterize said rigid member as a comparatively short member adapted to effectively with stand compressive stresses.

3. A thermostatic switch as defined in claim 1 wherein the connection between the substantially rigid member and the first flexible member is disposed in close proximity to the foot end of the housing, and the connection between said rigid member and the second flexible member is disposed approximately midway between the opposite ends of the housing so as to characterize said rigid member as a comparatively short member adapted to eflectively withstand compressive stresses, and wherein the switch contacts are resiliently biased into engagement with one another.

4. A thermostatic switch comprising a tubular housing made of material having a high coeflicient of expansion, an assembly of members disposed within said housing along the length thereof and made of a material having a relatively low coefficient of expansion, stop means for said assembly of members, and switch contacts carried by said assembly of members and engaging one another, said assembly including first and second laterally spaced flexible members anchored respectively to the head and foot ends of said housing, and a substantially rigid member extending from a free end portion of said first flexible member toward said housing head and second flexible member, one end portion of said rigid member being rigidly secured to said free end portion of said first flexible member and being movable therewith laterally away from said second flexible member and the opposite end portion of said rigid member being rigidly secured to an intermediate portion of said second flexible member and being movable therewith laterally away from said first flexible member, said switch contacts being mounted respectively on a free end portion of said second flexible member and an intermediate portion of said first flexible member at a substantial distance from said relatively rigid member, said housing being operative when it expands due to a rise in temperature above normal to turn said free end portions of the flexible members outwardly in opposite directions, and said stop means being adapted to limit the transverse movement of said free end portions of the flexible members so as to prevent excessive stressing of said flexible members when turned outwardly as aforesaid.

5. A thermostatic switch comprising a tubular housing made of material having a high coeflicient of expansion, an assembly of members disposed within said housing along the length thereof and made of a material having a relatively low coeflicient of expansion, and switch contacts carried by said assembly of members and engaging one another, said assembly including first and second laterally spaced flexible members anchored respectively to the head and foot ends of said housing, and a substantially rigid member extending from a free end portion of said first flexible member toward said housing head and second flexible member, one end portion of said rigid member being rigidly secured to said free end portion of said first flexible member and being movable therewith laterally away from said second flexible member and the opposite end portion of said rigid member being rigidly secured to an intermediate portion of said second flexible member and being movable therewith laterally away from said first flexible member, said switch contacts being mounted respectively on a free end portion of said second flexible member and an intermediate portion of said first flexible member at a substantial distance from said relatively rigid member, said second flexible member being provided with an integral base portion which extends in spaced relation around said free end portion of the first flexible member, said housing being operative when it expands due to a rise in temperature above normal to turn said free end portions of the flexible members outwardly in opposite directions, said base portion of the second flexible member and said housing being adapted to limit the transverse movements of said free end portions of the flexible members so as to prevent excessive stressing of said flexible members when turned outwardly as aforesaid.

6. A thermostatic switch comprising a tubular housing made of material having a high coeflicient of expansion, an assembly of members disposed within said housing along the length thereof and made of a material having a relatively low coefficient of expansion, and switch contacts carried by said assembly and resiliently biased into engagement with one another, said assembly including first and second laterally spaced flexible members, means adjustably anchoring said first flexible member to the head end of said housing, said second flexible member being fixedly anchored to the foot end of said housing, and a substantially rigid member extending from a free end portion of said first flexible member toward said housing head and second flexible member, one end portion of said rigid member being rigidly secured to said free end portion of the first flexible member and being movable therewith laterally away from said second flexible member and the opposite end portion of said rigid member being rigidly secured to an intermediate portion of said second flexible member and being movable therewith laterally away from said first flexible member, said switch contacts being mounted respectively on a free end portion of said second flexible member and an intermediate portion of said first flexible member at a substantial distance from said relatively rigid member, said adjustable means being operable to tension said flexible members and compress said substantially rigid member more or less to thereby selectively regulate the force with which said switch contacts normally engage one another, and said housing being operative when the temperature rises above normal to expand and thus increase the stresses in the members of said assembly to thereby turn said free end portions of the flexible members outwardly in opposite directions, said switch contacts being opened thereby at a predetermined temperature above normal.

7. A thermostatic switch as defined in claim 6 wherein the members of the assembly are flat bar members, the broad faces of the rigid member being positioned in opposed relation cach to a broad face of a flexible member, wherein the means adjustably anchoring the first flexible member to the head end of the housing comprises a pin rigidly secured to said first flexible member, and an adjusting screw threadedly engaged with said pin and the head end of said housing, the pitch of the threads whereby said pin and adjusting screw are engaged being greater than that of the threads whereby said adjusting screw and head end of the housing are engaged, and wherein said switch contacts have lead wires secured thereto and extending through said head end of the housing.

8. A thermostatic switch comprising a supporting structure formed of a material having a relatively high co etficient of thermal expansion, a pair of flexible strut members disposed in laterally spaced, substantially parallel relation within said supporting structure, one end of one of said members being secured to a corresponding end of said structure and the opposite end of the other of said members being secured to a corresponding opposite end of said structure, a relatively inflexible member interposed intermediate said flexible members, said inflexible member having its opposite ends so respectively secured to said flexible members as to dispose it in a plane extending obliquely with respect to the substantially parallel planes of said flexible members, one of said flexible members having a portion projecting freely beyond its point of securement to said intermediate inflexible member, said freely projecting portion of said one flexible member constituting a cantilever support for an electrical contact element, a contact element mounted on the free end of said cantilever support, and a coacting contact element operatively associated with said cantilever supported contact element.

9. In a thermostatic switch as defined in claim 8 wherein the obliquely extending plane of disposition of said relatively inflexible intermediate member intersects said one flexible member at a point substantially removed from the unsecured end of the latter.

10. A thermostatic switch comprising a frame member formed of material having a high coefficient of expansion, an assembly of members formed of material having a relatively low coelficient of expansion, and switch contacts carried by said assembly of members and engaging one another, said assembly including first and second elongated flexible members disposed in generally parallel laterally spaced overlapping relation with the two remote ends respectively of said flexible members anchored to 8 said frame member, and an elongated comparatively rigid member rigidly connected by one end to the free end portion of said first flexible member in the region of the anchorage for said secured flexible member and by the opposite end to an intermediate portion of said second 'lexible member, a substantial distance from the region of the anchorage for said second member, whereby said rigid member is positioned along a line extending through said first mentioned connection toward said second flexible member and away from the anchorage for said second flexible member, and whereby said rigid and first flexible members, in the region where the same are connected, are movable laterally away from said second flexible member, and said rigid and second flexible members, in

the region where the same are connected, are movable laterally away from said first flexible member, said switch contacts being mounted respectively on the free end portion of said second flexible member and an intermediate portion of said first flexible member at a substantial distance from said rigid member.

References Cited in the file of this patent UNITED STATES PATENTS 2,441,725 Smith May 18, 1948 2,627,565 Smith Feb. 3, 1953 2,660,646 Fritzinger Nov. 24, 1953 

